Three 4-week-old Yorkshire-Hampshire cross piglets from a litter of 9 (7 liveborn) developed convulsions the day of weaning. They were subsequently obtunded, ataxic, and hypermetric and had intention tremors. An affected male pig was presented live for necropsy on day 5 postweaning. This animal was euthanatized and necropsied. No significant grossly visible postmortem lesions were found. Histologic examination of the brain disclosed laminar necrosis of the submeningeal cerebral and cerebellar cortices with replacement by broad sheets of gitter cells. Occasional cerebral and cerebellar leptomeningeal and parenchymal vessels were surrounded by lymphocytes with fewer eosinophils. The morphologic diagnosis was severe multifocal subcortical cerebral and cerebellar laminar necrosis with moderate multifocal lymphocytic and eosinophilic cerebral and cerebellar leptomeningeal and parenchymal perivasculitis. The history and histologic findings are consistent with an etiologic diagnosis of sodium ion intoxication.